1. Field of the Invention
The present invention relates to the field of battery management, and more particularly to the field of battery management integrated circuits supporting portable devices. Specifically, the present invention relates to a low noise Charging method and device for portable devices.
2. Description of the Related Art
Generally, there are many charger ICs for Li-Ion or Ni—Cd batteries, starting form an external AD-DC adapter. Most of them use external power transistors to supply the charge current to the battery pack, which disadvantageously lead to large occupied area on the PCBs (printer circuit board).
A very popular approach is the linear charger, where a constant voltage current limited supply is used to charge the battery. The main drawback is that the serial regulator from the power supply has to be able to dissipate a large power. This implies the use of a big power transistor, which is not preferred in portable devices because of the large size and PCB area consuming.
There are other discrete solutions that use an external transistor to switch on and off, controlled by a microprocessor and additional circuitry to measure the battery voltage. These have the drawback of a high cost and a big PCB area. Still other solutions use a DC-DC buck converter to charge the battery. They have the drawback of a high noise generated in the system during charging, a high cost and special mechanical enclosures that have to be used to fulfill the EMI specifications. There are too some less expensive hysteresis chargers that have the drawback of a high noise generated at the end of charge. This perturbs the normal operation of the wireless portable devices.
Accordingly, there exists a need for a charging system or circuit which is able to overcome the above mentioned drawbacks.